This invention relates generally to flow proportioners and more particularly, it relates to a class of flow proportioners which obtain a signal indicating a characteristic of the rate of flow of a liquid, such as the level of liquid as it flows through a weir and corrects the signal for the shape of the weir or the flow path of the bed through which the fluid is flowing so that it represents the rate of flow of the fluid. The corrected signal is then integrated to provide another signal indicating the volume of liquid flowing past the flow proportioner. The signal from the integrator is, in some applications, used to actuate a fluid sampler at periodic increments of volume of fluid flowing through the flow proportioner.
In one type of prior art flow proportioners of this class, the signal indicating the rate of flow of the fluid moves an arm that rests against a mechanical cam. The mechanical cam lifts the arm close an electrical switch at certain points in each cycle of revolution, which points are selected on the cam to correct the signals for the shape of the flow bed.
This type of prior art flow proportioner has several disadvantages, such as: (1) the cams are mechanical and are of heavy weight, thus causing inaccuracies due to hysteresis; (2) a relatively large amount of power is necessary to operate the flow proportioner; (3) the flow proportioner is expensive because of a large number of relatively complicated and expensive parts; (4) it has to be supplied with power more frequently and does not run unattended for long periods of time; and (5) the output electrical signal is pulse-length modulated and this is a difficult signal to accurately handle for integration purposes.
These problems have been alleviated by a flow proportioner described in co-pending U.S. patent application Ser. No. 295,012 by Louis Franklin Lederer, assigned to the same assignee as the application and filed on Oct. 4, 1972, now U.S. Pat. No. 3,954,009. In this system, the signal indicating the height of the fluid is obtained by a float which positions an electrical stylus on a rotating disc at a radius from its center of rotation that is proportional to the height of the fluid. The rotating disc has a printed circuit upon it which is in circuit with the stylus and with a pulse generator so that pulses are applied to an output circuit during a portion of the time that the movable arm is in contact with the printed circuit. The printed circuit is shaped to correct for the shape of the flow path so that the number of output pulses are proportional to the rate of flow of the fluid. These output pulses are counted electronically to indicate the volume of fluid flowing past the flow proportioner.
However, this system is not without disadvantages since it is unable to provide a visible readout of indicia or manual controls which are readily adjustable for different units of measurement. Moreover, the flow proportioner described in U.S. patent application Ser. No. 295,012 requires substantial electrical power for operation, although less than some prior art flow proportioners, as well as being subject to wear, particularly electrical contact wear, and is not readily usable with some types of liquid height measuring devices.